The present invention relates generally to lasers. More particularly, the invention relates to semiconductor detectors for detecting the level of power output by semiconductor lasers.
One technique used to detect the power of a laser is an in-line external detector which interrupts light that emanates directly from the front or back facet of the laser. In the case of an independently addressable laser array, this in-line detector monitors the light emanating from the facets of all of the lasers in the array. The result of such a detection technique is that independent power control of each laser element is not possible. Therefore complicated methods involving the use of imaging optics to split light off from the forward or backward laser beam have been resorted to. However, the result is a cumbersome, inelegant, and delicate package that is not suitable for use in more integrated situations. Other disadvantages of in-line detection techniques exist. For example, the operation of the laser is directly interfered with as part of the beam must be channelled into the detector. This translates into reduced output efficiency.
In addition to in-line detection techniques, there have also been detectors implemented with reflectors to emit light from the laser in a direction vertical to the horizontal active layer of a semiconductor laser. For example, Scifres, et al., U.S. Pat. No. 4,633,476, discloses internal mirrors placed in the light path of the laser causing light to be reflected upwards and out of the semiconductor substrate. The light is then detected at the surface of the semiconductor device where it can be used to provide data regarding the power level of the laser.
Kobayashi, U.S. Pat. No. 4,674,100 is similar to Scifres in that it includes a detector which receives light diffracted from within the laser and then uses the level of this light to determine the power of the laser; However, like Scifres, Kobayashi provides the detector in a different level of the semiconductor material than that of the laser. Therefore, the laser and the detector have differing layer designs and also must be fabricated at different times.